In a typical radio communications network, communication devices, also known as mobile stations, wireless devices, wireless terminals and/or User Equipments, UEs, communicate via a Radio Access Network, RAN, to one or more core networks. The radio access network covers a geographical area which is typically divided into cell areas, with each cell area being served by a base station, e.g. a radio base station, RBS, which in some networks may also be called, for example, a “NodeB” or “eNodeB”. In this disclosure, the terms “network node”, base station” and “eNB” are used interchangeably to represent a node in the network that is capable of communication radio signals with a communication device. Further, the terms “communication device”, “UE” and “terminal” are used interchangeably to represent a communication device that is capable of communication radio signals with a network node of a radio access network.
A cell is a geographical area where radio coverage is provided by the radio base station at a base station site or an antenna site in case the antenna and the radio base station are not collocated. Each cell is identified by an identity within the local radio area, which is broadcast in the cell. Another identity identifying the cell uniquely in the whole radio communications network is also broadcasted in the cell. One base station may have one or more cells. A cell may be downlink and/or uplink cell. The base stations communicate over the air interface operating on radio frequencies with the user equipments within range of the base stations.
A Universal Mobile Telecommunications System, UMTS, is a third generation mobile communication system, which evolved from the second generation, 2G, Global System for Mobile Communications, GSM. The UMTS terrestrial radio access network, UTRAN, is essentially a RAN using wideband code division multiple access, WCDMA, and/or High Speed Packet Access, HSPA, for user equipments. In a forum known as the Third Generation Partnership Project, 3GPP, telecommunications suppliers propose and agree upon standards for third generation networks and UTRAN specifically, and investigate enhanced data rate and radio capacity. In some versions of the RAN as e.g. in UMTS, several base stations may be connected, e.g., by landlines or microwave, to a controller node, such as a radio network controller, RNC, or a base station controller, BSC, which supervises and coordinates various activities of the plural base stations connected thereto. The RNCs are typically connected to one or more core networks.
Specifications for the Evolved Packet System, EPS, have been completed within the 3rd Generation Partnership Project, 3GPP, and this work continues in the coming 3GPP releases. The EPS comprises the Evolved Universal Terrestrial Radio Access Network, E-UTRAN, also known as the Long Term Evolution, LTE, radio access, and the Evolved Packet Core, EPC, also known as System Architecture Evolution, SAE, core network. E-UTRAN/LTE is a variant of a 3GPP radio access technology wherein the radio base station nodes are directly connected to the EPC core network rather than to RNCs. In general, in E-UTRAN/LTE the functions of a RNC are distributed between the radio base stations nodes, e.g. eNodeBs in LTE, and the core network. As such, the Radio Access Network, RAN, of an EPS has an essentially “flat” architecture comprising radio base station nodes without reporting to RNCs.
TDD Configurations
FIG. 1 shows an example of a table of UL/DL subframe configurations according to 3GPP TS 36.211, version 12.3.0. Here, it should be noted that for UL/DL subframe configuration {0}, measurement gaps with offsets 3 and 8 subframes relative to the frame border will be squeezed in between two UL subframes. Moreover, it should also be noted that for UL/DL subframe configurations {0, 1 and 6}, measurement gaps with offsets 2 and 7 subframes will be squeezed in between a special subframe and an UL subframe.
Time Division Duplex, TDD
Transmission and reception from a node, e.g. a communication device in a cellular system such as LTE, can be multiplexed in the frequency domain or in the time domain, or combinations thereof. In Frequency Division Duplex, FDD, downlink and uplink transmission take place in different, sufficiently separated, frequency bands. In Time Division Duplex, TDD downlink and uplink transmission take place in different, non-overlapping time slots. Thus, TDD can operate in unpaired spectrum e.g. using the same frequency band for both downlink and uplink transmissions, whereas FDD requires paired spectrum using separate frequency bands for the downlink and uplink transmissions.
Typically, the structure of the transmitted signal in a communication system is organized in the form of a frame structure. For example, LTE uses ten equally-sized subframes of length 1 ms per radio frame. In case of FDD operation, two carrier frequencies may be used, one for uplink transmission, fUL, and one for downlink transmission, fDL. At least with respect to the communication device in a cellular communication system, FDD may be either full duplex or half duplex. In the full duplex case, a communication device may be able to transmit and receive simultaneously, while in half-duplex operation, the communication device is not able to transmit and receive simultaneously. A half-duplex communication device is monitoring/receiving in the downlink except when explicitly being instructed to transmit in a certain subframe. In case of TDD operation, there is only a single carrier frequency and UL and DL transmissions are always separated in time also on a cell basis. As the same carrier frequency is used for both UL and DL transmission, both the base station and the communication devices need to switch from transmission to reception and vice versa. According to an aspect of any TDD system is to provide the possibility for a sufficiently large guard time where neither DL nor UL transmissions occur. This is required to avoid interference between UL and DL transmissions. This guard time may be provided by special subframes, e.g. subframe 1 and, in some cases, subframe 6, which are split into three parts: a downlink part, DwPTS, a guard period, GP, and an uplink part, UpPTS. The remaining subframes are either allocated to UL or DL transmission.
TDD allows for different asymmetries in terms of the amount of resources allocated for UL and DL transmission, respectively, by means of different UL/DL configurations. In LTE, there are seven different configurations as shown in FIG. 1, which may be employed to achieve different amounts of resources for UL and DL transmission.
Dynamic TDD
In future radio communication networks, it is envisioned that there will be more and more localized traffic, where most of the communication devices will be operating in hotspots, or in indoor areas, or in residential areas. These communication devices may be located in clustered nature and may produce different UL and DL traffic at different times. This essentially means that a dynamic feature to adjust the UL and DL resources to instantaneous (or near instantaneous) traffic variations would be required in future local area cells. TDD has a potential feature where the usable band can be configured in different time slots to either the UL or DL. This allows for the above-mentioned asymmetric UL/DL allocation, which is a TDD-specific property not possible in FDD. As shown in FIG. 1, there are seven different UL/DL configurations in case of TDD, providing DL resources in the range of 40%-90%.
In current radio communication networks, the UL/DL configuration is semi-statically configured, which means that it may not match the instantaneous traffic situation. This will result in inefficient resource utilization in both UL and DL, especially in cells with a small number of communication devices. Thus, a “dynamic” TDD should be introduced to which may configure the TDD UL/DL subframe configurations according to current traffic situations in order to optimize user experience. Furthermore, such a “dynamic” TDD approach may also be utilized to reduce network energy consumption.
Existing radio communication networks employing TDD typically use fixed TDD UL/DL subframe configurations, where some subframes are always UL and some subframes are always DL. This limits the flexibility in adopting the UL/DL asymmetry to varying traffic situations.
One possibility to increase the flexibility of a TDD system, at least in some scenarios, is summarized below where each subframe (or part of a subframe) belongs to one of three different types:                Downlink subframes used (among other) for transmission of DL data, system information, control signaling and hybrid-ARQ feedback in response to uplink transmission activity. Here, the communication device is monitoring Physical Downlink Control CHannel, PDCCH, channel, i.e. the communication device may receive scheduling assignments and scheduling grants. Special subframes are similar to DL subframes except that in addition to the DL part, the special subframe also include a guard period, as well as, a small UL part in the end of the subframe to be used for random access or sounding.        Uplink subframes used (among other) for transmission of UL data, UL control signalling (e.g. channel-status reports), and hybrid-ARQ feedback in response to DL data transmission activity. Data transmission on the Physical Uplink Shared CHannel, PUSCH, in UL subframes are controlled by UL scheduling grants received on a PDCCH in an earlier subframe.        Flexible subframes, which also may be referred to as “Don't Know What They Are”, DKWTA, subframes, are possibly to use for UL or DL transmissions as determined by scheduling assignments/grants.        
In a dynamic TDD system, which also may be referred to as an enhanced Interference Mitigation and Traffic adaptation, eIMTA, system, a group of subframes are fixed subframes. This means that they are either UL or DL subframes in all radio frames, while others are flexible subframes, i.e. in some radio frames they may be UL subframes, while in other radio frames the same subframe may be a DL subframe or even special subframe. The assignment of the UL or DL direction is done in a dynamic manner on the basis of frame or multiple of frames. Flexible subframes are also called interchangeably as dynamic subframes. Throughout this disclosure, the term eIMTA generally indicates the use of UL/DL subframe configurations which contain at least one flexible subframe. The mechanism of this adaptation is explained in 3GPP TS 36.300, version 12.2.0.
For UL scheduling and HARQ timing, the communication device follows a predetermined reference UL/DL subframe configuration based on the UL/DL subframe configuration provided in System Information Block 1, SIB1. For DL HARQ timing, the communication device follows the reference UL/DL subframe configuration provided through dedicated signaling. DL subframes in the reference UL/DL subframe configuration provided in SIB1 remain unchanged, whereas only a subset of UL and special subframes may be reconfigured to DL subframes. In E-UTRAN, the network node may send a L1 signalling to the communication device on PDCCH on the PCell to indicate which UL/DL subframe configuration (defined in 3GPP TS 36.211, version 12.3.0) is currently used for one or more serving cell(s). This UL/DL subframe configuration provided by the L1 signalling applies for a Radio Resource Control, RRC, configured number of radio frames.
The periodicity of eIMTA configurations may be 10 ms, 20 ms, 40 ms, or 80 ms. The UE is configured to operate in eIMTA by means a so-called RRC information element, IE, defined in 3GPP TS 36.331, which is referred to as: